The United States consumes approximately 30% of the world's annual energy supply. About 93% of our energy requirements are provided by fossil fuels of which nearly half are from crude oil sources. Since crude oil production in the United States has been falling off since reaching a peak in 1972-1973, crude oil is supplied largely from the Middle East. Recent events in the Middle East have sharply focused our overdependence on foreign crude oil supplies and have made apparent our need to develop alternate energy sources. Thus, our attention has focused on finding renewable or noncritical forms of energy to replace our current foreign crude oil supplies.
Perennial growth matter such as wood, cotton trash, corn stalks, wheat chaff, forest residues, alfalfa, sunflower stalks, weeds, leaves, and other similar vegetation are in the category of renewable energy sources. Because of the ease with which sufficient renewable energy sources can be grown here in the United States, renewable energy sources have been receiving attention as a potential major source of energy.
Coal, once used as a major fuel source here in the United States long before the discovery of other fossil fuels, was displaced as a major fuel to a considerable degree for a number of years. However, because of its abundance here in the United States, coal is receiving renewed interest as a potential major source of energy because it is considered a noncritical energy form which can provide the energy required to sustain a reasonable standard of living while alternative sources of energy such as solar energy and nuclear energy can be perfected.
The wide spread utilization of coal as a major energy source or other renewable energy sources in the United States has been hampered by a lack of suitable means by which we directly convert these energy sources to useful work in such applications as automobiles, aircraft, locomotives, trucks, busses, electric generators, pumps, electric generating stations, etc. Although much research has been going on for years for transforming coal into other fuel forms, very little technical progress has been made to burn coal directly in internal combustion engines or increase the present use of coal burning furnaces because of the difficulty in burning coal rapidly and completely. The direct injection of solid pulverized fuels into an internal combustion engine or external combustion system dictates that the solid fuels be properly prepared prior to burning. Thus, it has been found that in order to burn solid fuels in internal combustion engines or external combustion systems, the solid fuels must be ground, shredded or pulverized to an appropriate particle size so that the solid fuels can be properly mixed with air so as to be burned quickly and completely in any combustion system.
There are several known prior art metering devices for solid fuels. For example, Steiger, U.S. Pat. No. 4,070,996, Rutz et al, U.S. Pat. No. 4,056,080 are directed to a reciprocating internal combustion engine which is fueled utilizing powdered fuel. Both of these devices utilize charged powdered coal which is injected or charged into the valve piston as the valve is opened to create an air blast for expelling the coal and air into the combustion chamber. In Lummis, U.S. Pat. No. 745,635, pulverized coal is utilized for the purpose of producing carbon monoxide.
Hardgrove, U.S. Pat. No. 2,275,394 and Havemann, U.S. Pat. No. 2,635,564 teach a combustion system for pulverized fuel. Specifically, Hardgrove teaches a pulverized fuel burning apparatus wherein bituminous coal is supplied as a function of steam load to a pulverizer. A fan providing carrier air moves the coal laden air through fuel supply lines to a fuel burning apparatus or furnace chamber of a steam generator. A secondary source of air is supplied through a wind box in a clockwise direction while a pair of fuel nozzles are arranged to supply a stream of fuel and air in a counter-clockwise direction. An adjustable blade impeller at the discharged end of the fuel nozzles enhances the mixing of the fuel stream with secondary air and the centrifugal effect of the primary fuel/air stream causes the larger coal particles to mix with the secondary air stream while the lighter particles remain in the primary air fuel stream. Havemann, U.S. Pat. No. 2,635,564 adapts a known vortex motion principle to impart a vortex motion to a primary air flow which is mixed with a secondary air flow containing fuel particles and preheated prior to being supplied to an injector system in a combustion chamber.
All of these prior art devices fail to produce a mixture of coal dust and air of proper proportions suitable for use in an appropriate combustion device so as to burn uniformly because the coal dust tends to cake and precipitate in the conduits and upon the seat of the charging valve. Furthermore, these prior art devices fail to evenly distribute the mixture before entering into the combustion chamber because the coal dust tends to agglomerate into balls of varying proportions. One prior art device which attempts to solve these problems in Holzwarth, U.S. Pat. No. 1,897,478. Holzwarth teaches an apparatus wherein a solid or solid fluid fuels are charged into constant volume combustion chambers associated with a turbine in such a manner that a completely uniform and homogeneous mixture of the fuels with the combustion supporting area is obtained. Holzwarth also teaches a safety mechanism to protect the charging devices against excessive and destructive pressures in the event of premature combustion or preignition of the fuel air mixture. Holzwarth's device, however, is very complex and expensive to make. In addition, Holzwarth must dilute the coal dust particles in a plurality of stages to uniformly suspend the particles in air.
Thus, none of the aforementioned designs provides a simple, inexpensive solid fuel particle and air metering device for mixing solid fuel particles with air in one stage to form a uniform air entrained mixture which does not agglomerate, cake or precipitate on the conduits prior to entering a suitable combustion device in gas turbines, diesels, Brayton cycles, stratified charge, Otto cycle, Sterling, free piston, Wankle, etc. or into an external combustion system such as a furnace.